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# Large-scale silicon quantum photonics implementing arbitrary two-qubit processing

## Abstract

Photonics is a promising platform for implementing universal quantum information processing. Its main challenges include precise control of massive circuits of linear optical components and effective implementation of entangling operations on photons. By using large-scale silicon photonic circuits to implement an extension of the linear combination of quantum operators scheme, we realize a fully programmable two-qubit quantum processor, enabling universal two-qubit quantum information processing in optics. The quantum processor is fabricated with mature CMOS-compatible processing and comprises more than 200 photonic components. We programmed the device to implement 98 different two-qubit unitary operations (with an average quantum process fidelity of 93.2 ± 4.5%), a two-qubit quantum approximate optimization algorithm, and efficient simulation of Szegedy directed quantum walks. This fosters further use of the linear-combination architecture with silicon photonics for future photonic quantum processors.

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## Acknowledgements

The authors thank S. Paesani, J. Silverstone, G. Sinclair, K. Aungskunsiri and C. Sparrow for helpful discussions and A. Murray and M. Loutit for assistance with wire-bonding the device. This work was supported by EPSRC programme grant EP/L024020/1, US Army Research Office (ARO) grant no. W911NF-14-1-0133, US Air Force Office of Scientific Research (AFOSR) and the Centre for Nanoscience and Quantum Information (NSQI). X.Q. acknowledges support from the China Scholarship Council and the National Natural Science Foundation of China (NSFC no. 61632021). X.Z. acknowledges support from the National Key Research and Development Program (2017YFA0305200 and 2016YFA0301700), the National Young 1000 Talents Plan, and the Natural Science Foundation of Guangdong (2016A030312012). J.W. acknowledges support from the National Young 1000 Talents Plan. T.C.R. acknowledges support from the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (project no. CE170100012). J.L.O.B. acknowledges a Royal Society Wolfson Merit Award and a Royal Academy of Engineering Chair in Emerging Technologies. M.G.T. acknowledges support from the ERC starter grant ERC-2014-STG 640079 and an EPSRC Early Career Fellowship EP/K033085/1. J.C.F.M acknowledges support from EPSRC Early Career Fellowship EP/M024385/1.

## Author information

Authors

### Contributions

X.Z., X.Q., T.C.R., J.L.O.B. and J.C.F.M. conceived and designed the project. X.Z. and X.Q. designed the device. X.Q., J.W., C.M.W., L.K., G.D.M. and R.S. built the experimental set-up and carried out the experiments. X.Q., X.Z., T.L., S.O.G., J.B.W. and J.C.F.M. performed the theoretical analysis. X.Z., J.L.O.B., M.G.T. and J.C.F.M. managed the project. All authors discussed the results and contributed to writing the manuscript.

### Corresponding authors

Correspondence to Xiaoqi Zhou or Jonathan C. F. Matthews.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Supplementary information

### Supplementary Information

Supplementary notes and figures.

## Rights and permissions

Reprints and Permissions

Qiang, X., Zhou, X., Wang, J. et al. Large-scale silicon quantum photonics implementing arbitrary two-qubit processing. Nature Photon 12, 534–539 (2018). https://doi.org/10.1038/s41566-018-0236-y

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• DOI: https://doi.org/10.1038/s41566-018-0236-y

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